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New Installation/Pump Question(s)

We currently pump water from and underground spring out from under our basement into a 500 gal. holding tank buried next to our house. I purchased a 1.5 HP Wayne lawn sprinkler pump http://www.waynepumps.com/prodlist.asp?pcode=WLS150 to help water our lawn using the water in the tank.

I currently have a cheap 4 head garden hose manifold attached to the pump. Each hose has two above-ground impact sprinklers attached. I tried 3 on each but there wasn't enough pressure in the line to drive the third. I can run the pump for approximately 20-30 minutes which pumps the tank down to within a foot of the bottom. The people at Wayne told me that this particular pump shouldn't run any less than 4 hoses.

I'm hoping to make this a permanent installation by next summer. How do I begin determining how many sprinkler heads I can have on each run of hose assuming that I replace the garden hoses with regular underground irrigation piping?

Your Wayne pump is a standard design, with no built-in injector for increased output pressure. It could empty that tank in less than ten minutes, if you ran it at the flow and pressures where it is most efficient. For lawn sprinkling use, a shallow-well jet pump is what you want. If you were stuck using that pump you linked, you could reliably do so by employing oversized piping, and the one sprinkler head that can run at low pressures with good coverage, the Rainbird R-50. That head has a manually-adjustable stator, unlike the automatic ones in regular gear-drive rotors, so you can make the head rotate reliably at pressures under 25 psi, and with your pump pushing over 40 gpm at low pressure, you could run more than 20 heads simultaneously.

You may never see such a system, because it needs pipe sizes as large as 2 inches or more to eliminate loss of pressure at these high flows. {If your pump is centrally located, you can branch out from the pump with several smaller pipes, but never with anything as small as a garden hose - there are tables on pressure losses in pipe, according to pipe size and flow amount, to help you select proper pipe sizes} Another reason you may not see many, if any, low-pressure/high-flow sprinkler systems is that the sprinklers don't spray as far at low pressures (and the R-50 is just like the rest of them) so you wind up needing more heads.

And this is where I get more confused. Since we knew nothing about these systems and no one seemed to be able to help I naturally looked for a "lawn sprinkler" pump. So if Wayne sells this model as a pump for lawn irrigation, then why does it sound (by you description) that it is less than ideal for the task at hand?

Second question: can you list any particular pumps that would be better suited?

There was once a time when lawn sprinkler systems were installed with brass mist heads running at 20 psi, and for that application, you have a 'lawn sprinker' pump. But for rotor heads that are going to shoot 35 feet or more, with 40 psi running pressure, you won't get as much bang for your buck. Your best pumps are not going to come from Sears or Home Depot, but from a well water supplier near you. I favor Goulds pumps, because of their performance and construction. Their cast-iron shallow-well jet pumps start at around four hundred bucks list price. I count on them for years of trouble-free performance.

Maybe your lawn doesn't need sprinklers shooting thirty-five feet. Nothing prevents you from using as many sprinkler heads as it takes to get coverage at low pressure. Besides the R-50, another Rainbird head that functions at low pressures is their Maxipaw impact rotor, which will also perform at less than 30 psi (at certain pressures, it's easily the head with the best spray distance, although you need to break up the spray to even out the coverage) - Pros don't favor the head, because sealed case rotors have a better reliability record. Doesn't mean it won't work reliably enough for home use.

But even with the low pressure Rainbird R-50, it sounds as if the installation won't be a picnic, requiring rather large diameter pipes. Might I be better off (in the long run) trying to sell the existing pump and getting what I need? The Wayne lawn sprinkler pump only cost me $125.00 so it may be worth it to sell it and get what will function better and be a better installation.

It depends. A pro won't do it, because they will use less sprinklers spaced further apart, using higher pressure and smaller-diameter pipe which can be pulled underground with a machine. It's different for a homeowner digging trenches by hand. A trench is a trench, whether you drop a one inch pipe in it or a two inch pipe. You really have to take the time to design the layout of your intended system, to see what head placements and spray distances work for you.